The invention relates to a swing bridge for converting the rotary motion of an eccentric driven by a motor shaft into a reciprocating motion of a power output for a tool in electrically powered appliances, consisting of a bridge yoke comprising the power output and mounted on two film hinges, with walls disposed perpendicularly thereto and with a connecting rod coupled to the swing bridge and the eccentric and aligned parallel to the bridge yoke.
Such swing bridges are known from German OS No. 21 17 319 and German AS No. 27 49 936 and are used primarily in dry shavers; however they are also suitable for electrical massagers, toothbrushes, and files.
In designing swing bridges for the requred swing amplitude, certain dimensioning rules have also been maintained for the connecting rod to ensure the required rigidity in the swing direction and flexibility transversely thereto. However, in an attempt to observe these rules, connecting rod dimensions frequently result which are suitable only for relatively large span widths of the swing bridge between the film hinges serving as supporting elements, or folded designs result (German AS No. 27 49 936 and German No. 05 29 10 469) which tend not only to have increased space requirements widthwise but also have a tendency toward frequency-dependent instabilities which can be controlled only at increased expense and with close tolerances. In addition, the arrangement of the motor in the housing, which depends on the point of coupling between its eccentric and the connecting rod head, complicates the installation and arrangement of the other necessary electrical components in the housing.
A swing bridge is known from Japanese Utility Model No. Y2-58-5585, wherein the bridge yoke consists of a plate provided with a power output and strip-shaped film hinges formed thereon, as well as a connected rod formed eccentrically on the plate. In order for the connecting rod formed laterally on the plate to execute a motion corresponding to the eccentric stroke, a bulge is provided in the long side of one of the strip-shaped film hinges. By virtue of the direct forming of the film hinges and the connecting rod on the plate and the lateral bulge in one of the film hinges, the resultant bridge yoke exhibits unstable behavior and tends toward uncontrolled movements which result in losses of the useful linear working movement.
German OS. No. 29 10 469 teaches a swing frame with a swing beam supported on the housing by two pairs of flexibly elastic strips. The flexibly elastic strips of each pair of strips are coupled together by webs in FIG. 6 whereby an additional web can be provided to stabilize the two pairs of strips. The connecting rod which urges the swing beam into an oscillating motion is part of an additional swing frame consisting partially of flexibly elastic strips and formed on the swing beam. However, as a result of the deformation of the flexibly elastic pairs of strips connected with the swing beam, no exact linear motion of the swing beam is ensured in the devices according to this known publication.
The goal of the invention is therefore to provide a swing bridge in which the disadvantages of devices according to the state of the art do not exist and wherein greater freedom in the arrangement and dimensions of all the named components with respect to the requirements stated hereinabove is ensured and by means of which the rotary movement of an eccentric driven by a motor shaft is optimally converted into a linearly reciprocating motion.
According to one advantageous embodiment of the invention, the connecting rod engages the wall located opposite the wall provided with the opening.
The rigidity of the swing bridge can be further increased according to the invention by the rigid unit being reinforced by at least one strip and a web.
Advantageously the swing bridge is mounted suspended in the housing, whereby the pressure exerted on the drive by connected tools is advantageously accepted by the strip-shaped film hinges without deformation thereof.
Advantageously the swing bridge is mounted suspended in the housing, whereby the pressure exerted on the drive by connected tools is advantageously accepted by the strip-shaped film hinges without deformation thereof.